If you want to make issues available as an in-app purchase, you will need to create a separate in-app purchase entry in iTunes Connect for each of the issues or collections you want to offer. Note that the in-app purchase type for issues/collections needs to be 'Non-Consumable'.

Enter a reference name (that will be used for reporting purposes only), e.g. Twixl Magazine October 2014

In the Product ID field, enter a unique identifier that will be used for reporting. It can be composed of letters and numbers. Usually this will also be a reverse DNS name like the app identifier: e.g. com.casablancapublishing.rickscafe.oct2014

Set pricing for the issue/collection by selecting a price tier

Provide in-app purchase information for at least one language.

Adding issues as in-app purchases in the Twixl Distribution Platform

For each of the in-app purchases defined in iTunes Connect, you also need to add issues/collections in the Twixl Distribution Platform, and select "Purchase" as the issue type.

IMPORTANT:

Make sure the product identifier in the Twixl Distribution Platform matches exactly with the one you defined in iTunes Connect.

In-app purchase testing

In order to test in-app purchases with an Ad Hoc build of your app, Apple provides a sandboxing environment. To do this:

Build and install an Ad Hoc version of your app.

Create a test user in iTunes Connect.

Logout from the iTunes and App Store for your regular account.

Try to make a purchase and login with the test user you created.

You should be able to make the test purchase in the testing ('sandbox') environment.